Recent interest in the adaptive response of strain-sensitive musculoskeletal tissues has led to the development of various devices aimed at delivering well controlled mechanical stimuli to laboratory cell culture preparations. In many of these devices, the targeted cells are adhered to the surface of a compliant substrate membrane, which, in turn, undergoes cyclic transverse displacements, induced either by imposed pressure differentials or by direct platen contact. In such "cell stretching" systems, it is assumed that the induced substrate deformation is the dominant mechanical stimulus delivered to the target cells. However, almost no attention has been directed to the potentially severely confounding effects of reactive shear and/or normal stresses imparted to the adhered cells due to the coupled motion of the overlying fluid medium. The applicants have developed a preliminary finite element model of one representative, widely-used cell stimulus system. By means of a specially instrumented testing chamber, they have shown that the finite element formulation reasonably models the culture substrate's motions and deformation, both statically and under complex dynamic loading conditions. Detailed stress distribution data from that finite element model strongly suggest that there are many situations in contemporary cell culture practice wherein the cell strains induced by coupled motions of the nutrient medium may be of at least the same order of magnitude as the cell deformations induced by the input membrane strains. The preliminary finite element model appears to accurately simulate the major inertial effects present in the nutrient medium. However, as presently formulated, that model has no provision to estimate fluid shear stress, likely also an important stimulus for cellular mechano- transduction. For that reason, the investigator proposed (Aim 1) to amend their constitutive treatment of the nutrient medium - for simplicity, initially modeled as a very compliant hyperplastic continuum - to address the considerably more complex behavior of a Newtonian fluid. A set of physical validation experiments is planned, including both substrate and fluid kinematics (Aim 2). They then will use this physically validated finite element model plus a spatially refined near- surface model to identify specific experimental conditions under which the stress state of cells adhered to the membrane culture surface becomes appreciably influenced by the kinetics of the nutrient medium of the present system (Aim 3), as well as for several other mechano- stimulus system designs (Aim 4). Finally, for the present system at selected operation settings above and below the computed fluid-influence threshold(s), they will conduct cell culture experiments to detect differentials of biological response, monitoring cyclin D1 and DNA synthesis (Aim 5). If coupled nutrient medium motions can indeed induce biologically consequential reactive strains to cells in culture, then it is very important to identify the operational conditions under which such an effect occurs.